1. Field of the Invention
The present invention relates to a tie-bar less clamping apparatus for an injection molding machine.
2. Description of the Related Art
In a generally known tie-bar less clamping apparatus, a stationary platen is fixedly held on one end of a frame, a movable platen is supported on the other end of the frame by a clamping mechanism for opening, closing and clamping a mold. Since the movable platen is connected to the stationary platen only by the frame without using any tie bars, clamping force is born only by the frame. The tie-bar less clamping apparatus not provided with any tie bars facilitates access to the mold and work for changing the mold. Therefore, the tie-bar less clamping apparatus is applied to small injection molding machines. On the other hand, the frame is distorted asymmetrically when the mold is clamped by the tie-bar less clamping apparatus because it is not provided with any tie bars. Consequently, the movable and the stationary mold cannot be held in a parallel positional relation, and clamping force is exerted unevenly on the mold.
Prior art clamping apparatus to solve such problems is proposed in JP B2 No. 121,543/1995. In a prior art clamping apparatus disclosed in this cited reference, a stationary platen and/or a clamping mechanism is pivotally supported on a frame so that the parallel positional relation between a stationary mold and a movable mold can be maintained even if the frame is bent. Another prior art technique proposed in this cited reference supports a movable platen so as to be tiltable on guide rails disposed on the frame by a spring suspension mechanism to maintain the parallel positional relation between the stationary mold and the movable mold. (Refer to AT-B No. 402,811/1997 which corresponds to the above Japanese patent publication.)
The foregoing prior art clamping apparatus has a complicated construction and requires difficult mold changing work.